For felt-tip, fiber-tip and other capillary writing instruments, generally pens and markers, it is desirable to provide a cap which is capable of indicating that the cap has been firmly and fully applied to the writing tip of the instrument and thus which can serve as an assurance that the tip will not dry out.
To this end it has been proposed to provide a cap internally with a longitudinally shiftable insert which is displaceable between two abutments, one position serving to indicate that the cap has been properly applied to the tip whereas the other represents the position in which the tip has been withdrawn from the cap.
A writing instrument having a shiftable insert is described in U.S. Pat. No. 2,808,670 in which the insert is a cylinder sleeve which is pressed into the first position by a compression spring received in the cap and becomes effective when the cap is withdrawn from the instrument.
The insert in this position projects from the cap and provides a view of a free surface which can be formed with an image.
Upon application of the cap to the instrument, the insert is shifted inwardly by an abutment surface on the tip of the writing implement. The compression spring is stressed and the image-carrying surface is obstructed by the cap. The fastening of the cap in place is effected via a screw thread which also takes up the prestressing force of the spring. The purpose of this cap is to provide an image or other visible character when the cap is removed from the writing implement, the image or character serving to inspire the writer. This system does not, therefore, provide a signal for the complete sealing engagement of the cap on the writing implement since the image is uncovered by the cap even before the tip has been fully sealed by the cap.
The protective cap for a fiber marker or writing implement (German Utility Model No. DE-GM 74 21 165) can be provided with a forward portion which lies upon the writing tip after application of the cap, and has a surface which is visible, transparent or the like to permit the writing color to be readily recognized, thereby eliminating any need for special coloration of the cap. The interior of the transparent portion of the cap can be easily covered with the writing color so that the actual position of the point or tip within the cap cannot be determined.
In this case, although a proper sealing signal might be given, frequently such a signal is not given and it is not possible to determine whether a cap has been properly seated upon the tip of the writing implement.